Relevant parts of this prior art description are also a part of embodiments of the invention.
Several floor panels on the market are installed in a floating manner with mechanical locking systems formed at the long and short edges. These systems comprise locking means, which lock the panels horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the panel. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminium or plastic material, which is integrated with the floor panel, i.e. joined with the floor panel in connection with the manufacture thereof.
Laminate flooring usually comprise a 6-8 millimetre, mm, wood based core, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1 mm thick lower balancing layer of laminate, plastic, paper or like material. A laminate surface comprises melamine-impregnated paper. The most common core material is fibreboard with high density and good stability usually called HDF—High Density Fibreboard. The impregnated paper is laminated to the core with heat and pressure. HDF material is hard and has a low flexibility especially in the vertical direction perpendicular to the fibre orientation.
Recently a new type of powder based laminate floors, generally referred to as WFF floors (Wood Fibre Floors), have been introduced. Impregnated paper is replaced with a dry powder mix comprising wood fibres, melamine particles, aluminium oxide and pigments. The powder is applied on an HDF core and cured under heat and pressure. Generally, high quality HDF is used with a high resin content and low water swelling. Advanced decors may be formed by means of digital printing. Water based ink may be injected into the upper surface of the powder or injected in several transparent powder layers prior to pressing such that a very wear resistant 3D-print may be obtained. A digital binder and powder printing generally referred to as the “BAP method” may also be used to create advanced 3D-prints. Pigmented powder, or so-called dry ink, may be bonded in several layers with a digitally applied binder pattern comprising blank ink without pigments. The high wear resistance is often used to produce copies of stone and tiles. Such WFF floors may be rather wide and the material cost for the short edge locking system may be rather high.
LVT flooring with a thickness of 3-6 mm usually comprises a transparent wear layer which may be coated with an ultra-violet, UV, cured polyurethane, PU, lacquer and a decorative plastic foil under the transparent foil. The wear layer and the decorative foil are laminated to one or several core layers comprising a mix of thermoplastic material and mineral fillers. The plastic core is generally soft and very flexible.
Wood Plastic Composite floors, generally referred to as WPC floors, are similar to LVT floors. The core comprises thermosetting material mixed with wood fibre fillers and is generally stronger and much more rigid than the mineral based LVT core.
Thermoplastic material such as polyvinyl chloride, PVC, polypropylene, PP, or polyethylene, PE, may be combined with a mix of wood fibres and mineral particles and this may provide a wide variety of floor panels with different densities and flexibilities.
Moisture resistant HDF with a high resin content, LVT floors and WPC floors comprise stronger and more flexible core materials than conventional HDF based laminate floors and they are generally produced with a lower thickness.
A minimum thickness in several of the above mentioned floor types are mainly required in order to form the locking system. The panel itself is generally strong and flexible and a thickness of about 3-5 mm would in many applications be sufficient but cannot be used since it is not possible to form strong locking systems in such thin floors.
The above mentioned floor types comprise different core materials with different flexibility, density and strengths. Locking systems must be adapted to such different material properties in order to provide a strong and cost efficient locking function.